Systems and methods for peak junction temperature sensing and thermal safe operating area protection

ABSTRACT

A peak junction temperature monitoring system for a semiconductor device includes a peak power dissipation sensor for sensing the peak power dissipation in the device. A temperature sensor senses an average temperature of the device, and a peak junction temperature computation circuit generates a signal representative of a peak junction temperature based on input from the peak power dissipation sensor and the temperature sensor.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. patent application Ser. No.61/524,666, filed Aug. 17, 2011 the contents of which are incorporatedherein in their entirety.

COLOR PHOTOGRAPH STATEMENT

The patent application file contains at least one drawing executed incolor. Copies of this patent application publication with color drawingis provided herewith with payment of the necessary fee.

FIELD OF THE INVENTION

The present disclosure is generally related to systems and methods forpeak junction temperature sensing and thermal safe operating area (SOA)protection. The invention has particular utility in connection withsemiconductor devices, and particularly amplifier driver devices, andwill be described in connection with such utility, although otherutilities are contemplated.

BACKGROUND OF THE INVENTION

Amplifier output stages are frequently subjected to safe operating area(SOA) violations while driving loads in many applications. During an SOAviolation, the peak junction temperature of the driver device exceedsthe absolute maximum junction temperature of the driver device and cancause device destruction.

A conventional method to protect against SOA violations is to use atemperature sensor near the output driver device. The temperature sensorsenses an average temperature in the vicinity of the output driver butis not able to sense and report the peak temperature excursions.

FIG. 1 is a plot showing the difference between the temperatures 10sensed by such known temperature sensors in the vicinity of the outputdriver, and the actual temperature 11 of the driver device, when theoutput driver is subjected to large pulse power dissipation that causesan SOA violation. The actual temperature (11) of the driver device ismeasured using a thermal IR camera. As shown in FIG. 1, the temperature10 sensed by the temperature sensor generally differs by at least 50-80°C. from the actual peak junction temperature (11), depending upon powerdissipated, e.g., as measured by thermal IR camera. If the absolutemaximum junction temperature is 150° C., which is a typical figure formany output driver devices, an SOA violation is not detected by thetemperature sensor as shown in FIG. 1, even though the actual junctiontemperature exceeds 150° C.

Another method for protecting against SOA violations involves the use ofan embedded temperature sensor. However, there are at least two majordisadvantages to the embedded temperature sensor approach. First, suchmethods are generally specific to high power bipolar processors. For aDMOS (Double-Diffused-Metal-Oxide Semiconductor) process, the embeddedtemperature sensor is very difficult to implement and is prone to falsetrip and latch up issues caused by triggering of parasitic junctions.Secondly, depending upon layout, the embedded temperature sensor mayalso suffer from significant inaccuracies in measured temperature, ascompared to the actual peak junction temperature. FIG. 2 shows a thermalsimulation using finite element analysis (FEA) at 18 W peak powerdissipation for an exemplary output driver device with an embeddedtemperature sensor in the center of the device. As shown in FIG. 2, thetemperature 21 sensed by the embedded temperature sensor is 113.4° C.,while the maximum actual peak junction temperature 22 is 129.4° C. Thus,the temperature 21 sensed by the embedded temperature sensor is at least16° C. lower than the actual peak junction temperature 22.

Overcurrent protection is another known technique in amplifiers forprotecting the output devices against SOA violations. However,overcurrent protection or current limiting is generally not adequate toprotect against SOA violations. In many applications using reactiveloads, load current and output voltage can have an out-of-phaserelationship or phase delay between them. Thus, an SOA violation canoccur at much lower output current levels that are well below theovercurrent trip threshold if there is a higher voltage across theoutput driver device.

Thus, a need exists in the industry to address the aforementioneddeficiencies and inadequacies.

SUMMARY OF THE INVENTION

Systems and methods for peak junction temperature sensing and thermalSOA protection for a semiconductor device are disclosed. Brieflydescribed, in architecture, one embodiment of the system, among others,can be implemented as follows. The system contains a peak powerdissipation sensor configured to sense the peak power dissipation in thedevice and outputs a signal representative of the sensed peak powerdissipation. A temperature sensor is configured to sense an averagetemperature of the device and outputs a signal representative of theaverage temperature. A peak junction temperature computation circuit isconfigured to receive the signals from the peak power dissipation sensorand the temperature sensor, and generate a signal representative of apeak junction temperature based on the received signals.

In a further embodiment, systems for detecting thermal safe operatingarea violations for a semiconductor device are disclosed. The systemincludes a peak power dissipation sensor configured to sense the peakpower dissipation in the device and output a signal representative ofthe peak power dissipation. A temperature sensor is configured to sensean average temperature of the device and output a signal representativeof the average temperature. A maximum allowable peak power dissipationdetermining circuit is configured to determine a maximum allowable peakpower dissipation based at least in part on the signal representative ofthe average temperature, and to output a signal representative of themaximum allowable peak power dissipation. A comparator is configured tocompare the signal representative of the peak power dissipation with thesignal representative of the maximum allowable peak power dissipation,and to output a signal indicative of a thermal safe operating areaviolation if the peak power dissipation exceeds the maximum allowablepeak power dissipation.

Methods for monitoring a peak junction temperature in a semiconductorare also disclosed. In this regard, one embodiment of such a method,among others, can be broadly summarized by the following steps: sensinga peak power dissipation in the device; sensing an average temperatureof the device; and generating a signal representative of a peak junctiontemperature based on the sensed peak power dissipation and averagetemperature.

Methods of detecting a thermal safe operating area violation in asemiconductor device are further described. In this regard, oneembodiment of such a method, among others, can be broadly summarized bythe following steps: sensing a peak power dissipation in the device;comparing the sensed peak power dissipation with a signal representativeof a maximum allowable peak power dissipation; and generating a signalindicative of a thermal safe operating area violation if the peak powerdissipation exceeds the maximum allowable peak power dissipation.

In yet another aspect, a semiconductor chip that includes asemiconductor device having a peak power dissipation sensor configuredto sense the peak power dissipation in the device and output a signalrepresentative of the peak power dissipation is disclosed. A temperaturesensor is configured to sense an average temperature of the device andoutput a signal representative of the average temperature. A peakjunction temperature computation circuit is configured to receivesignals from the peak power dissipation sensor and the temperaturesensor, and to generate a signal representative of a peak junctiontemperature based on the received signals.

In a further embodiment, a semiconductor chip that includes asemiconductor device having a peak power dissipation sensor configuredto sense the peak power dissipation in the device and output a signalrepresentative of the peak power dissipation is disclosed. A temperaturesensor is configured to sense an average temperature of the device andoutput a signal representative of the average temperature. A maximumallowable peak power dissipation determining circuit is configured todetermine a maximum allowable peak power dissipation based at least inpart on the signal representative of the average temperature, and tooutput a signal representative of the maximum allowable peak powerdissipation. A comparator is configured to compare the signalrepresentative of the peak power dissipation with the signalrepresentative of the maximum allowable peak power dissipation, and tooutput a signal indicative of a thermal safe operating area violation ifthe peak power dissipation exceeds the maximum allowable peak powerdissipation.

Other systems, methods, features, and advantages are or will becomeapparent to one with skill in the art upon examination of the followingdrawings and detailed description. It is intended that all suchadditional systems, methods, features, and advantages be included withinthis description, be within the scope of the present invention, and beprotected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the invention can be better understood with reference tothe following drawings. The components in the drawings are notnecessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the present invention. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1 is a plot illustrating the difference between the temperaturessensed by prior art temperature sensing techniques and the actualtemperature of the driver device.

FIG. 2 illustrates a thermal simulation for an output driver device withan embedded temperature sensor in the center of the device, as known inthe prior art.

FIG. 3 is an illustration of a first exemplary block diagram of a peakjunction temperature monitoring system for a semiconductor device.

FIG. 4 is an illustration of a block diagram of the peak powerdissipation sensor of the system shown in FIG. 3.

FIGS. 5a and 5b are plots illustrating the linearity of the peak powerdissipation sense signal in relation to the actual peak powerdissipation through the device, in accordance with the system shown inFIG. 3.

FIG. 6 is a plot illustrating the substantially linear correlationbetween ΔT (ΔT=T_(J)−T_(AVG)) and peak power dissipation through thedevice (PD_PK) with changing pulse power widths as well as repetitivepulse power, in accordance with the system shown in FIG. 3.

FIGS. 7a-c are plots illustrating the temperature difference (ΔT)between the peak junction temperature (T_(J)) and the sensed averagetemperature (T_(AVG)) with differing applied pulse widths and pulsepower, in accordance with the system shown in FIG. 3.

FIG. 8 is an illustration of a block diagram of the peak junctiontemperature computation circuit of the system shown in FIG. 3.

FIG. 9 is a plot illustrating the computed value of peak junctiontemperature (T_(J)) superimposed over the actual peak junctiontemperature, in accordance with the system shown in FIG. 3.

FIG. 10 is an illustration of a second exemplary block diagram of athermal SOA violation detection system.

FIG. 11 is a plot illustrating simulation results for a circuitimplementation of the system of FIG. 10.

FIG. 12 is a flowchart illustrating a method of monitoring a peakjunction temperature in a semiconductor device, in accordance with thesystem of FIG. 3.

FIG. 13 is a flowchart illustrating a method of detecting a thermal safeoperating area violation in a semiconductor device, in accordance withthe system of FIG. 3.

DETAILED DESCRIPTION

FIG. 3 is an illustration of a first exemplary block diagram of a peakjunction temperature monitoring system 100 for a semiconductor device.The system 100 contains a peak power dissipation sensor 110, atemperature sensor 120 and a peak junction temperature computationcircuit 130.

The peak power dissipation sensor 110 receives signals representative ofvoltage across the output driver device and current through the outputdriver device and senses the peak power dissipation in the output driverdevice in real time when the amplifier is operational. The output of thepeak power dissipation sensor 110 is a signal (e.g., current signalI_(PD) _(_) _(PK) _(_) _(SENSE)) that represents the peak powerdissipated in the output driver device. This signal is input into thepeak junction temperature computation circuit 130, which computes thepeak junction temperature based on the signal representative of the peakpower dissipation and the signal representative of the averagetemperature, received from the temperature sensor 120.

The temperature sensor 120 is located in the vicinity of the outputdriver device, but is not embedded into the output driver device. Thereis no specific, required location for the temperature sensor 120 (i.e.,no specific distance from the driver device on a chip) in order tomeasure an “average temperature,” as disclosed herein. Rather, thetemperature sensor 120 may be located anywhere such that it can sense atemperature of the device. For example, the temperature sensor 120 maybe located on a chip somewhere in the general vicinity of the device. Aswill be further described herein, in particular with respect to FIGS. 6and 7 a-c, the peak power dissipated (PD_PK) in the driver device may belinearly correlated with the temperature difference (ΔT) between thepeak junction temperature (T_(J)) and the measured average temperature(T_(AVG)). The peak junction temperature (T_(J)) may be calculated,using the linear correlation, based on sensed peak power dissipation andthe sensed averaged temperature. Thus, it is not critical that thetemperature sensor 120 be located in any specific position or distancefrom the output driver device, as the peak power dissipation (PD_PK) andthe temperature difference (ΔT=T_(J)−T_(AVG)) may still be correlatedand used to compute the peak junction temperature (T_(J)) based on thesensed peak power dissipation (PD_PK) and average temperature (T_(AVG)).

The temperature sensor 120 may be any type of sensor for sensing atemperature of a driver device. The temperature sensor 120 senses anaverage temperature of the device, and outputs a signal representativeof the sensed average temperature to the peak junction temperaturecomputation circuit 130. The peak computed junction temperature (T_(J))is computed by the peak junction temperature computation circuit 130,based on the signal received from the temperature sensor 120 and thesignal received from the peak power dissipation sensor 110. The peakjunction temperature computation circuit 130 is further described below,particularly with respect to FIG. 8.

The peak junction temperature computation circuit 130 may generate asignal representative of the computed peak junction temperature, whichmay be input into a comparator 140, which compares the computed peakjunction temperature (T_(J)) with a maximum allowable peak junctiontemperature, and may generate a signal indicating an SOA condition ifthe computed peak junction temperature (T_(J)) exceeds the maximumallowable temperature.

FIG. 4 is an illustration of a block diagram of the peak powerdissipation sensor 110 of the system 100 shown in FIG. 3. The peak powerdissipation sensor 110 includes a current sensor 112 and a voltagesensor 114.

The current through the output device 111 is sensed by the sense device113 and input into the current sensor 112. The output (e.g., I_(MON)_(_) _(N+)) of the current sensor 112 is a signal representative of thecurrent through the output device 111 (e.g., lo-side driver deviceM_(N+)) when the amplifier is operational. The voltage sensor 114 sensesthe voltage across the device 111 (M_(N+)).

The output (e.g., I_(DS+) _(_) _(N+)) of the voltage sensor 114 is asignal representative of the voltage across the device 111 (M_(N+)). Thesignal representative of the current through the output device 111,output from the current sensor 112 (I_(MON) _(_) _(N+)), and the signalrepresentative of the voltage across the device 111, output from thevoltage sensor 114 (I_(DS) _(_) _(N+)), are multiplied by amultiplication element 116. The resulting signal, output from themultiplication element 116, is a signal (I_(PD) _(_) _(PK) _(_)_(SENSE)) which is representative of real-time peak power dissipation inthe device 111 (M_(N+)). This signal may be a voltage signal (e.g.,V_(PD) _(_) _(PK) _(_) _(SENSE)), which may be converted into a currentsignal (e.g., I_(PD) _(_) _(PK) _(_) _(SENSE)) through avoltage-to-current converter 118. The multiplication element 116 may beany known circuit element for multiplying signals, including forexample, an electronic mixer for producing an output signal equal to theproduct of the two input signals.

FIGS. 5a and 5b are plots demonstrating the linearity of the peak powerdissipation sense signal (shown in volts on the y-axis), i.e. the signalrepresentative of the peak power dissipation through a device (e.g.,device 111 in FIG. 4), in relation to the actual peak power dissipationthrough the device (shown in watts on the x-axis). The actual peakdissipated power through the device may be measured using any knownpower dissipation measurement techniques, for example, by using testinstruments to directly measure current and voltage through the device.The sense signal representative of the peak power dissipation throughthe device may be, for example, a voltage signal (e.g., signal V_(PD)_(_) _(PK) _(_) _(SENSE) in FIG. 4) or a current signal (e.g., I_(PD)_(_) _(PK) _(_) _(SENSE) in FIG. 4).

In the example shown in FIG. 5a , the sense signal is a voltage signaland the output current is fixed at 1 A. As the peak dissipated powerincreases (x-axis), for example, by increasing the drain-to-sourcevoltage across the device, while keeping the output current fixed at 1Amp, the sensed voltage (y-axis) increases linearly. That is, the sensesignal is linearly proportional to the actual, measured peak powerdissipated through the device, and the relationship between the sensesignal and the actual peak power dissipation may be expressed as:Sense Signal=1/M*Peak Power Dissipation,

where M is a scaling factor or M-factor, for example in W/mV, which maybe the reciprocal of the slope of the line relating the sense signal tothe measured peak power dissipation.

As shown in the example of FIG. 5a , the slope equals 31.6 mV/W, and Mis 1/31.6 W/mV. Thus, a sense signal of 10 mV would represent a peakpower dissipation of 0.316 Watts. The M-factor may be set to a desiredvalue, for example, by selecting a sense device 113 that passes a verysmall amount of current, as compared to the current through the outputdevice 111. For example, the sense device 113 may be a sense MOSFET thatpasses a very small amount of current proportional to the current in theMOSFET output device 111. As shown in FIG. 4, the drain, source and gatevoltage may be the same on both the output device 111 and the sensedevice 113. Additionally, or alternatively, the M-factor may be adjustedto any desired value utilizing current sense resistors or other currentsense techniques known in the relevant field.

FIG. 5b , like FIG. 5a , is a plot demonstrating the linearity of thepeak power dissipation sense signal in relation to the actual peak powerdissipation through the device. In FIG. 5b , the output current is setat 4 Amps. The slope equals 31.5 mV/W, and M is 1/31.5 W/mV. Thus, evenwith an output current set at four times higher than in the plot of FIG.5a , the slope of the line remains essentially the same. That is, thesense signal remains linearly proportional to the actual peak powerdissipated through the device at a higher output current, with the sameslope, and for a wide range of power dissipation. While there is somerange of non-linearity in both FIGS. 5a and 5b (particularly at veryhigh peak power dissipation), these ranges are not of interest as theylikely are outside of the operating range of the output device 111, andthus likely will not be experienced in the output device 111.

FEA simulation and thermal camera data show that the relationshipbetween ΔT (ΔT=T_(J)−T_(AVG)) and peak power dissipation through thedevice 111 (PD_PK) is substantially linear with changing pulse powerwidths as well as repetitive pulse power, as can be seen from FIG. 6.The data shown in the plot of ΔT versus peak power dissipation in FIG. 6were collected and analyzed for pulse widths ranging from 1 ms to 10 msand pulse power ranges from 5 W to 20 W (see FIGS. 7a-c ). This rangewas determined based upon the range of temperatures that produce SOAviolations for audio output devices; however, any other range may be ofinterest, depending upon the application, and the relationship betweenΔT and peak power dissipation through a device may accordingly bederived and utilized for any such desired range of SOA violations. Thepeak power dissipation (PD_PK) was measured using instruments (e.g.,voltage and current probes) to measure the peak power dissipationthrough the output device in real-time. The peak junction temperature(T_(J)) was measured using a thermal camera, and the average temperature(T_(AVG)) was sensed using a temperature sensor 120 located in thevicinity of the output device 111.

FIGS. 7a-c are plots showing the temperature difference (ΔT) between thepeak junction temperature (T_(J)) and the sensed average temperature(T_(AVG)) with differing applied pulse widths and pulse power. FIG. 7ais a plot of ΔT (ΔT=T_(J)−T_(AVG)) versus time (ms) for an applied 18 Wpeak pulsed power with pulse widths: of 1 ms (line 201), 2 ms (line 202)and 2.88 ms (line 203). ΔT for each applied 18 W peak pulse hassubstantially the same maximum value 210. Thus, there is substantiallyno inaccuracy in the measurement of ΔT, regardless of the pulse width,for an applied 18 W peak power pulse.

FIG. 7b is a plot of ΔT (ΔT=T_(J)−T_(AVG)) versus time (ms) for anapplied 5 W peak pulsed power with pulse widths: of 1 ms (line 301), 2ms (line 302), 2.88 ms (line 303) 5 ms (line 304) and 10 ms (line 305).ΔT for each applied 5 W peak pulse has a slightly different maximumvalue 310. Thus, there is some, but not substantial, inaccuracy in themeasurement of ΔT, depending on the pulse width of the applied 5 W peakpower pulse. The worst case inaccuracy of ΔT, as seen in FIG. 7b , isabout 6.5° C. That is, with an applied 5 W pulse having a pulse width of1 ms, the maximum difference (ΔT) between the peak junction temperature(T_(J)) (e.g., as measured by a thermal camera) and the sensed averagetemperature (T_(AVG)) (e.g., as sensed using a temperature sensor 120located in the vicinity of the output device 111) is about 6.5° C. lessthan the maximum difference (ΔT) between the peak junction temperature(T) and the sensed average temperature (T_(AVG)) for an applied 5 Wpulse having a pulse width of 10 ms.

FIG. 7c is a plot of ΔT (ΔT=T_(J)−T_(AVG)) versus time (ms) for anapplied 18 W repetitive peak pulsed power with pulse widths: of 1 ms(line 401), 2 ms (line 402) and 2.88 ms (line 403). ΔT for each applied18 W peak pulse has multiple maxima, with the maxima for each pulsewidth having substantially the same maximum value. For example, for theapplied 18 W repetitive peak pulse having a 2 ms pulse width (line 402),ΔT has two maximums 410, both having the same value.

By measuring the peak dissipated power and the corresponding ΔT (e.g.,as shown in FIG. 6), and/or by measuring ΔT in response to a known,applied peak pulse power (e.g., as shown in FIGS. 7a-c ), a relationshipbetween ΔT and peak power dissipation may be derived, and ΔT can beapproximated to be linear with changing peak power dissipation.

FIG. 8 is an illustration of a block diagram of the peak junctiontemperature computation circuit 130. The peak power dissipation sensesignal (I_(PD) _(_) _(PK) _(_) _(SENSE)) is used to calculate ΔT(ΔT=T_(J)−T_(AVG)). As discussed above, the linear relationship betweenpeak power dissipation and ΔT may be derived and known. The peak powerdissipation sense signal is input into an amplifier or gain block 135,which applies a gain to the signal of K₂/K₁, where K₂ is the slope ofthe line correlating ΔT=T_(J)−T_(AVG) with peak power dissipation (e.g.,as shown in FIG. 6), and K₁=1/M, where M is a scaling or M-factor, forexample as discussed above with respect to FIGS. 5a and 5b . The outputof the gain block (ΔT=T_(J)−T_(AVG)) is summed by summation element 137with T_(AVG), sensed by the temperature sensor 120, which results in asignal representative of T_(J), the peak junction temperature.

Utilizing the peak junction temperature computation circuit 130 shown inFIG. 8, FIG. 9 is a plot 900 showing the computed value of peak junctiontemperature (T_(J)) 501 superimposed over the actual peak junctiontemperature 502, as measured by a thermal camera, resulting from theapplication of a 14 W pulse having a pulse width of 10 ms. The units ofthe y-axis of the plot are degrees Celsius (° C.) and the units of thex-axis of the plot are milliseconds (ms). As seen in FIG. 9, thecomputed peak junction temperature 501 is almost identical to theactual, measured peak junction temperature 502 for substantially theentire duration of the application of the 10 ms, 14 W pulse (i.e., from0 to 10.00 ms on the x-axis). The computed peak junction temperature 501differs somewhat from the measured peak junction temperature 502 atlower temperature regions 505 (e.g., below about 80° C.); however, atsuch regions the possibility of SOA violation is very unlikely, and suchlow-temperature differences between computed peak junction temperature501 and measured, actual peak junction temperature 502 are of little orno concern.

FIG. 10 is an illustration of a second exemplary block diagram of athermal SOA violation detection system 600. The system 600 may beimplemented on a chip. Unlike the system 100 of FIG. 3, where peakjunction temperature is computed, the system 600 of FIG. 10 does notdirectly compute a peak junction temperature (e.g., by summing ΔT withT_(AVG)). Rather, the thermal SOA violation detect system 600 of FIG. 10compares a signal 601 representative of peak power dissipation with asignal 602 representative of a maximum allowable peak power dissipation.The comparator 603 outputs a signal 604 which indicates whether thesensed peak power dissipation exceeds the maximum allowable peak powerdissipation, and if so, generates a signal indicative of a SOAviolation.

The signal representative of maximum allowable peak power dissipation(I_(PD) _(_) _(PK) _(_) _(MAX)) 602 is computed in real time usingT_(AVG), T_(JMAX) and slope K₂. A signal 610 representative of theaverage temperature (T_(AVG)) is input from a temperature sensor 120 andis subtracted by a difference element 611 from a signal 612representative of a maximum allowable peak junction temperature(T_(JMAX)). The signal 612 representative of a maximum allowable peakjunction temperature (T_(JMAX)) may be selectively adjustable torepresent any desired maximum peak junction temperature (T_(JMAX)), forexample, by adjusting the current output from the current source 613.

The output of the difference element 611 is a signal 614 representativeof ΔT (=T_(J)−T_(AVG)) which is multiplied by multiplication element 616with a signal 615 representative of 1/K₂, where K₂ is the slope of aline correlating ΔT with peak power dissipation. The output signal 602of the multiplication element 616 is thus a signal representative of themaximum allowable peak power dissipation, and is input to the comparator603.

For each device, for example, for each audio driver output device withina channel, sensed signals representative of current 620 a-d and voltage621 a-d are input into a respective multiplication element 622 a-d. Theoutput from each multiplication element 622 a-d is input into a maximumpower dissipation determining circuit 624, which determines which of theinput signals represents the largest peak power dissipation through adevice, and outputs that signal 601. The signal representative of thepeak power dissipation 601 is input to the comparator 603. Thecomparator 603 compares the signal representative of the peak powerdissipation 601 with the signal representative of the maximum allowablepeak power dissipation 602, and outputs a signal 604 indicative ofwhether a SOA violation has occurred. For example, the comparator 603may output a logical “1” if the signal 601 exceeds the maximum allowablepeak power signal 602, thereby indicating that a SOA violation hasoccurred. The comparator 603 may output a logical “0” if the signal 601does not exceed the maximum allowable peak power signal 602, therebyindicating that no SOA violation has occurred.

Simulation results using actual circuit implementation are shown in FIG.11. The simulation is run using T_(AVG)=25, 85 and 125° C., with thedrain-to-source voltage of the output device (V_(DS)) held at a maximumvoltage of 40V and the load current is swept from −3 A to +3 A. In allthree cases (i.e., T_(AVG)=25, 85 and 125° C.), the maximum allowablepeak junction temperature (T_(JMAX)) is programmed to be 150° C. Thecalculated signal representative of the maximum allowable peak powerdissipation (I_(PD) _(_) _(PK) _(_) _(MAX)) 602 decreases withincreasing temperature (and increasing sensed T_(AVG)) and correlateswith measured thermal camera data.

FIG. 12 is a flowchart 1200 illustrating a method of monitoring a peakjunction temperature in a semiconductor device, in accordance with thefirst exemplary system in FIG. 3. It should be noted that any processdescriptions or blocks in flow charts should be understood asrepresenting modules, segments, portions of code, or steps that includeone or more instructions for implementing specific logical functions inthe process, and alternate implementations are included within the scopeof the present invention in which functions may be executed out of orderfrom that shown or discussed, including substantially concurrently or inreverse order, depending on the functionality involved, as would beunderstood by those reasonably skilled in the art of the presentinvention.

As is shown by block 1202, the peak power dissipation in the device 111is sensed. The peak power dissipation may be sensed by a peak powerdissipation sensor 110, which may output a signal representative of thepeak power dissipation in the device. An average temperature of thedevice 111 is sensed (block 1204) by a temperature sensor 120, which maybe located in the vicinity of the device 111. The temperature sensor 120may output a signal representative of the sensed average temperature.The temperature sensor 120 may be a non-embedded sensor. Based on thesensed peak power dissipation and average temperature, a signalrepresentative of a peak junction temperature is generated (block 1206).The signal representative of a peak junction temperature may begenerated by a peak junction temperature computation circuit 130 whichreceives the signal representative of the sensed peak power dissipationand the signal representative of said average temperature, and generatesthe signal representative of the peak junction temperature based on thereceived signals. The signal representative of the peak junctiontemperature may be compared with a signal representative of a maximumallowable junction temperature, and it may be determined whether thepeak junction temperature exceeds the maximum allowable junctiontemperature.

FIG. 13 is a flowchart 1300 illustrating a method of detecting a thermalsafe operating area violation in a semiconductor device, in accordancewith the second exemplary system in FIG. 10. As is shown by block 1302,the peak power dissipation in the device is sensed. The sensed peakpower dissipation 601 is compared with a signal representative of amaximum allowable peak power dissipation 602 (block 1304). Thecomparison may be performed by a comparator 503, which may generate asignal indicative of a thermal safe operating area violation if the peakpower dissipation exceeds the maximum allowable peak power dissipation(block 1306).

The signal representative of a maximum allowable peak power dissipationit 602 may be generated by computing a difference between a signalrepresentative of a maximum allowable peak junction temperature 612 andthe sensed average temperature 610, and multiplying the difference witha signal representative of the reciprocal of the slope of a line whichcorrelates the difference between peak junction temperature and averagetemperature with peak power dissipation 615. The average temperature maybe sensed by a non-embedded sensor. The signal representative of amaximum allowable peak junction temperature may be selectivelyadjustable.

It should be emphasized that the above-described embodiments of thepresent invention, particularly, any “preferred” embodiments, are merelypossible examples of implementations, merely set forth for a clearunderstanding of the principles of the invention. Many variations andmodifications may be made to the above-described embodiments of theinvention without departing substantially from the spirit and principlesof the invention. All such modifications and variations are intended tobe included herein within the scope of this disclosure and the presentinvention and protected by the following claims.

What is claimed is:
 1. A semiconductor chip comprising: a semiconductordevice; a peak power dissipation sensor configured to sense the peakpower dissipation in the device and output a signal representative ofsaid peak power dissipation; a temperature sensor configured to sense anaverage temperature of the device and output a signal representative ofsaid average temperature; a maximum allowable peak power dissipationdetermining circuit configured to determine a maximum allowable peakpower dissipation based at least in part on said signal representativeof said average temperature, and to output a signal representative ofthe maximum allowable peak power dissipation; and a comparatorconfigured to compare said signal representative of said peak powerdissipation with said signal representative of the maximum allowablepeak power dissipation, and to output a signal indicative or a thermalsafe operating area violation if the peak power dissipation exceeds themaximum allowable peak power dissipation.
 2. The semiconductor chip ofclaim 1, wherein said maximum allowable peak power dissipationdetermining circuit comprises: a difference element configured toreceive a signal representative of a maximum allowable peak junctiontemperature, and said signal representative of said average temperature,and to output a signal representative of a difference between saidreceived signals; and a multiplication element configured to multiplythe difference signal with a signal representative of the reciprocal ofthe slope of a line which correlates the difference between peakjunction temperature and average temperature with peak powerdissipation.
 3. The semiconductor chip of claim 2, wherein the signalrepresentative of a maximum allowable peak junction temperature isselectively adjustable.
 4. The semiconductor chip of claim 1, whereinthe maximum allowable peak power dissipation determining circuitdetermines the maximum allowable peak power dissipation in real-time. 5.The semiconductor chip of claim 1, further comprising: a plurality ofpeak power dissipation sensors, each configured to sense the peak powerdissipation in a respective device; and a maximum power dissipationdetermining circuit, configured to receive from each of said pluralityof peak power dissipation sensors a signal representative of said peakpower dissipation, and to output to said comparator the signalrepresentative of the largest sensed peak power dissipation.
 6. Thesemiconductor chip of claim 1, wherein the temperature sensor is anon-embedded sensor.
 7. The semiconductor chip of claim 1, wherein thedevice comprises a driver device for an audio amplifier.